Compact one-base type fluorescent lamps in which a plurality of glass tubes are connected with bridges to form a discharge path are known from Japanese Design Registration Nos. 861,419 and 970,929.
The bridge connection of the glass tubes of such a fluorescent lamp is performed by the method shown in Japanese Patent Application (Tokko Sho) No. 63-49334.
That is, a portion of the outer surface of a glass tube for bridge connection is heated and softened, and a gas is supplied into the glass tube to subject the glass tube to a high pressure so as to form an opening portion that protrudes outward in the softened portion. This glass tube is located adjacent to another glass tube having a similarly formed opening portion in such a manner that their opening portions face each other, and the opening portions are welded to each other so as to form a bridge portion.
For connecting three or more of glass tubes with bridges, first, many dual tubes, each of which is connected with a bridge as described above, are manufactured. Then, the dual tubes are connected with a bridge in turn by the same method. Alternatively, a required number of glass tubes are connected with a bridge one by one in turn by the above method.
As described above, in order to connect glass tubes with a bridge, the steps of heating, softening, opening, welding, bridge formation and the like should be performed in turn. For industrial bridge connection, a device for performing the steps is necessary. Furthermore, if the number of bridge connections increases, the number of steps that are required to complete a fluorescent lamp increases accordingly, thereby further complicating the device.
For example, when dual tubes that are formed by connecting two glass tubes with a bridge are connected with a bridge in turn for a plurality of times as described above, the device becomes complicated and large, thereby increasing the number of steps, the working time, and the cost. In addition, variations in the size, accuracy, and strength of the bridge portions of the product are large. Therefore, the quality of the product is not stable, and problems in quality and a decrease in yield increase the cost. The above problems are especially significant in a fluorescent lamp having more than four glass tubes and more than two dual tubes.